Yes I know that.... I am actually using only one pre-regulator feeding the two boards and have been using that setup in other situations (my power amp for instance) but would like to profit from some better crosstalk isolation. The trouble is I am actualy working on a very tight budget and can not get another TX in the near future so I found this idea in the ESP pages.... Power Supply for Power Amplifiers
What bothers me more is that I can not identify the extra GND loop when going from one single prereg to two preregs in parallel using the same TX.

Just one more question Frans, in your double mono schematic (two tx) I see you do not connect both grounds (left and right) together.

Also you do not make any reference to the output connections, so I admit we can leave both channels running completely independent without any common reference between them. What if there is a slight voltage difference between both channels grounds... does it procuce a current flowing in the output interconnects ? (I assume both output negatives will be joined inside the following preamp / power amp).

That’s right (spotted) and it is wrong (drawn). Check this out here is an updated (again) drawing In this new arrangement for 2 TX's the circuit/signal-ground is only connected (left to right) in the attached amplifier, no loops possible any ware. Your concern about voltage differences is cared for by the RX, RXL and RXR resistors.